Unsymmetrically substituted triazacyclohexanes and their chromium complexes

The unsymmetrically N-substituted N,N′-Ar2-N″-R-1,3,5-triazacyclohexanes 1–4 (Ar = ortho- or para-fluorophenyl, R = n- or iso-propyl) can be obtained in good yields from a one-step condensation reaction with excess amine. Solid state structures of 1–4 resemble closely those of their triaryl-substituted analogues. The condensation reaction to 4 was looked at by detailed NMR investigations and revealed that amine/aniline exchange is occurring in solutions containing free aniline even at ambient conditions setting up an equilibrium between all possible symmetrical and unsymmetrical triazacylcohexanes. Selective crystallisation of 4 from the solution drives the reaction to high yields of 4. Complexes 1–4 react readily with CrCl3 or CrCl3(THF)3 to form the corresponding CrCl3 complexes. The complexes are insoluble in non-polar solvents and decompose under decomplexation in coordinating solvents.

Graphical abstractUnsymmetrically substituted alkyl-bis(aryl) triazacyclohexanes were obtained by selective crystallisation from equilibrated mixtures. Reactions of these ligands with chromium trichloride afforded pure, but insoluble (TAC)CrCl3 complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide